Carb Mixture Screw Settings On A 790cc Bonnie With Tor's Anyone?

Trying to get my latest 2001 Bonnie as sweet running as possible. Initially she was really 'grumpy' cutting out if you cracked the throttle too hard while in neutral and stuttering at low revs on the move. This was dramatically improved but not totally eradicated by setting the mixture screws to around four turns out where, with a factory setup, around two and a half turns is recommended IIRC. Given that the bike came with a DNA filter, TTP air intake , and has had the AI removed using the TTP removal kit and a Triumph TORS exhaust fitted I am assuming that it has had a TTP stage 1 tune. Would this sort of mixture screw setting be normal for this sort of setup? How many turns have others found neccessary with a similar setup.

 

Thanks for that tuning information pdf Martin I will give that a good read. I am starting to think it is time to take the carbs off and give them a thorough inspection to see if there is something there that is 'hinky'. I guess I am coming up against the one really tricky part of buying a bike that someone has modified from stock in that, unless you get thorough and detailed notes on what has been done you can be left scratching your head as to what is going wrong. Looking at the chart in that document it would appear that the only thing that should have changed is the main jets. I guess the next step will be taking the carbs off and giving them a thorough inspection and clean and finding out what has been changed in them. Never come across this particular behaviour before and it's got me a little baffled. I am thinking about putting a pair of stock end cans (snapped up a pair to use for MOT's if neccessary for £20 off gumtree along with a gasket set, rear light cluster and new unused coils!) and the original snorkel and air filter that came with the bike on to see if it is the 'tune' that is causing the problem before taking the next step of taking the carbs off and giving them a going over.

 

The screws on the carbs have already been changed over to stainless by the previous owner. Vacuum caps look OK but not harm in getting new ones I think.

 

A question for all who have a 790cc Bonnie and who have fitted TOR's or Norman Hyde Togas plus new filters and removal of snorkel. Did you have to change your Pilot jets?

Still trying to get to the bottom of the 'stutter' on this 2001 Bonnie. Boning up on carb operation and thinking through what is going I am thinking that it seems to me that the most likely thing is that the removal of the snorkel/ fitting of TTP stage one tune and performance exhausts has left the bike choking up in the idle to 4000rpm where the pilot jets are in charge. Looking over the notes that a previous owner made on the tuning of my other Bonnie it states that they replaced the standard Pilot Jets (40's) with mixture screws at four turns with 42's and then took the mixture screws done to three turns. Certainly increasing the fuel in the mix via the mixture screws being turned out to 4 or more turns seems to eliminate the stutter.

I would be interested to know if anyone else had to increase their pilot jet size and, if so, what to, before I rip the carbs off and order new screws.

 

Unfortunately all I know is that the Stage one kit involves removal of the snorkel, fitting of a DNA air filter and 'Breathe' air filter cover and a 'Dyno developed jetting kit'. I will have to take the carbs apart in order to see what jets were fitted. According to the pdf that MadMrB provided further up the page they recommend that Pilot jets are upped to 42 from the standard 40 but I'm not sure if that applies with the TTP kit and TOR's exhaust.

The plugs are a little bit dark suggesting she is running rich but that may be down to me turning up the mixture to try and beat the stutter. I am getting the feeling that I may well be returning this one to stock to see if it cures the problem but that will require finding out what monkeying around has been done inside the carbs and shelling out for jets. Got a pair of standard silencers though and the original filter and intake with snorkel came with the bike.

 

I can't deny that I have been hoping for a quick fix as I want to get on with getting this one dressed up in a new set of bodywork and trying to get her out on what few dry days this year has left to offer and don't really fancy monkeying around back and forwards trying to get her to behave herself.

The websites like TTP imply that you buy their kit, bung it on and all is sorted but I have to say that, studying the history that came with my other 790 Bonnie she was back and forward a number of times changing main jets and adjusting mixture screw settings and changing to 42 pilots from 40's before she was sorted to the nice sweet running machine she is.

 

I am a bit puzzled by what you say about your bike bogging down at 80mph @Ben1307 and I don't think that would have anything to do with the mixture screws which, as shown in the graph in the Jenks document that @MadMrB shared only affect fuel supply between Idle and around half throttle. Is there a particular rev range that you find bad in all gears or is it only in a certain gear at 80mph?

I am surprised that your mixture screw is stuck and the bike is running at all. If it was all the way in (tightened up) you would be starving that carb of fuel at idle and I don't think the bike would actually idle without a lot of difficulty. Certainly when I turn an idle screw all the way in on my Bonnie she conks out.